It''s not the solicitor''s fault that your spouse has been stalling for a number of months. Take some comfort in the fact that the Nisi application is now being processed and things are moving forwards - albeit at a slower pace than you would have hoped for.
I really don''t think this is a battle worth fighting - you would be better spending your energy on sorting out the finances and tying up any other loose ends. You can''t change the date the Nisi application was actually sent, and pursuing this will only create additional stress and conflict and divert your attention away from other matters.
It''s a wise man (or woman) who knows when to keep their powder dry for a more appropriate battle.